Conventionally, polyvinyl alcohol (hereafter often abbreviated as PVA) is frequently used as a dispersant, an adhesive, a sizing agent, a film, a paper processing agent, a coating agent, etc. in various kinds of fields. For example, the use of partially saponified PVA as a coating agent is known, since it has water-solubility and film-forming property. However, when PVA is used in a spray method, which is a usual coating method, significant spinnability of PVA makes coating difficult (PVA is sprayed into a spiderweb form, not into a fine mist); thus the use of PVA as a coating agent in a spray method is hardly given a practical application.
In order to solve the above-mentioned problem, a coating composition comprising a PVA copolymer as a main component is suggested in WO 2005/019286 and JP-A 2007-22938. These documents also disclose a method for coating a pharmaceutical preparation such as a tablet, a granule, a fine granule, etc. with an aqueous solution of the above-mentioned coating composition. However, this method has problems: while the coating agent is sprayed, each unit of such a tablet, granule, or fine granule combines and sticks together, and subsequently the film coating peels back; in particular, when the spray rate of the coating solution is increased, the coating yield significantly decreases, and consequently a longer coating time is required.